The invention relates to an in-focus indicator for a camera, and more particularly, to such an indicator for use in a camera having a detector circuit capable of detecting a forward or backward focussing or an in-focus condition of the camera and in which the achievement of an in-focus position is audibly indicated.
The present inventor has previously proposed an in-focus indicator in which status signals of different levels are produced for a forward and a backward focussing of a taking lens so that an in-focus condition is annunciated in terms of sound and light when a switching between the levels of the both signals occurs (see Pending Japanese Patent Application No. 42,715/1981). Resort to the auditory sense, in addition to the vision, by providing an element capable of producing sound upon reaching an in-focus condition, is very effective in view of a focussing operation during which a photographer concentrates his attention to a principle object being photographed which is visible through a finder. However, the indicator suffers from the difficulty that the sound produced, indicating an in-focus condition, each time the camera moves through the in-focus point either forwardly or rearwardly as a result of a hand shake after the taking lens has once been adjusted to the in-focus position is annoying to a photographer himself as well as to adjacent personnel, and also renders a person being photographed to be too aware to permit a photograph in a natural condition from being taken.
On the other hand, it will be appreciated a slight degree of forward or backward focussing does not present a problem whatsoever so far as the practice of a taking picture is concerned, and a sharp photograph can be taken within a limited in-focus zone. Hence, it will be seen that when the sound is utilized to notify the in-focus position, it is desirable that the number of times the sound is produced be minimized by preventing the sound from being produced if the focal point moves across the in-focus position as long as the point is within an in-focus zone, after the in-focus position is once reached to permit the element to produce sound for a given time interval.